1. Field of the Invention
The present invention generally relates to a technology of a flat panel display; more specifically, to a method of driving a field sequential display apparatus.
2. Description of Related Art
In conventional liquid crystal displays, the light source designs of backlight modules usually do not venture far from white light sources (usually white light emanating from cold cathode tubes). The white light usually passes through color filters to form the backlight source needed for each of the pixels. From the perspective of an array of pixels, there is a red color filter, a green color filter, and a blue color filter above each pixel. This arrangement not only results in high production costs, but also gives rise to color deviation problems at the adjacent boundaries of each of the red, green, and blue color filters. In addition, since liquid crystal displays are manufactured with color filter structure, the white light sources experience brightness degradation due to light blockage at the color filters.
In view of the above problems, the color sequential display, which has complementary circuitry based on the Color Sequential Method, is developed. This type of display is also called the field sequential display because color fields are alternately displayed. The field sequential display uses various color light-emitting diodes (LEDs) to replace the conventional white light source. Color of each pixel is displayed by alternately lighting one of the color light sources according to the timing control. The corresponding theory is that in the short span of human visual retention, the rapidly switched red, green, and blue colors on the time axis mix to produce a color mixing effect. Consequently, the human eye experiences full color images.
FIG. 1A is a schematic view illustrating the driving waveform of a conventional field sequential display. As shown in FIG. 1A, a full frame includes a red, green, and blue fields. In the red field, red LEDs are lit to provide red backlights. During the T1 period, the field sequential display sequentially drives scan lines SL1˜SLn and writes the corresponding pixel data into each pixel. In addition, to avoid conflicts of the pixel data written by the red field with the next field (e.g. the green field), scan lines SL1˜SLn are simultaneously driven during the period T2, and the reset pixel data is written (e.g. black pixel data). In the green field and the blue field, green LEDs and blue LEDs are lit to provide green and blue backlights. The driving scheme of the scan lines SL1˜SLn in the green and blue fields is the same as the driving scheme of the scan lines SL1˜SLn in the red field. Nevertheless, the aforementioned driving method is a sequential driving scheme and coupled with the response times is needed for liquid crystal pixel light transmissions, therefore, the above-mentioned driving method results in lower light transmission quantity at the scan line SLn than at the scan line SL1. Consequently, the brightness of the displayed image brightness is not uniform.
A method to solve the problem aforementioned is disclosed in U.S. Pub. No. 2005/0225545A1, in which a liquid crystal display apparatus and its corresponding driving method are described. FIG. 1B is a driving waveform illustrating the driving scheme of the liquid crystal display apparatus found in U.S. Pub. No. 2005/0225545A1. As shown in FIG. 1B, in this disclosure, each field is separated into two sub-fields. Each of the sub-fields includes a write period 101, a display period 102, and a reset period 103. For the red field, the write period 101 of the first sub-field appears in each scan line to write pixel data in each pixel. The display period 102 appears after the pixel data is written in the last scan line for display. Although this driving scheme improves the uniformity of image brightness, there are still variations between the brightness of each scan line. In the reset period 103, each pixel is reset, avoiding conflicts of the pixel data written in this sub-field with the next sub-field.
In the second sub-field of the red field, the appearance order of the write period 101 is reversed compared to the order in the first sub-field. This driving scheme produces higher pixel brightness at the last scan line than the pixel brightness at the first scan line. The brightness displayed by pixels on each scan line is more uniform due to the write periods appearing in reverse order between the red field's first sub-field and second sub-field. The driving waveforms for the green field and the blue field are equivalent to those of the red field, and so descriptions can be referenced to the above.
Nevertheless, because two reset periods 103 appears in the same field, and the last scan line on which pixel data is written in has a display period 102, there is a squeezing effect for the write period 101. Consequently, the write period 101 is shortened. Due to current display panels increasing in size, the write period 101 is increasingly shortened. If the driving scheme disclosed in U.S. Pub. No. 2005/0225545 A1 is implemented on large display panels, there can be insufficient time in the write period 101 to accurately write in the pixel data.